U.S. patent number 5,752,162 [Application Number 08/552,424] was granted by the patent office on 1998-05-12 for methods for assigning subscriber units to visited gateways.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Peter Joseph Armbruster, Steven Harry Moritz, Steven Paul Sawyer.
United States Patent |
5,752,162 |
Sawyer , et al. |
May 12, 1998 |
Methods for assigning subscriber units to visited gateways
Abstract
Methods (100) assign a subscriber unit (30) to be served by a
gateway (40) based on such factors as the location of the
subscriber unit (30), whether the call is to be intercepted and
whether the serving gateway (40) is capable of servicing the
connection request. The method (100) does not drop a call because
the visited gateway initially assigned by the home gateway (40) is
unable to service the connection request; but instead routes the
call around disabled or congested gateways to an alternate visited
gateway that is capable of servicing the connection request.
Inventors: |
Sawyer; Steven Paul (Fountain
Hills, AZ), Armbruster; Peter Joseph (Tempe, AZ), Moritz;
Steven Harry (Phoenix, AZ) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
24205278 |
Appl.
No.: |
08/552,424 |
Filed: |
November 3, 1995 |
Current U.S.
Class: |
455/13.1;
455/450; 455/428 |
Current CPC
Class: |
H04B
7/18556 (20130101) |
Current International
Class: |
H04B
7/185 (20060101); H04B 007/185 () |
Field of
Search: |
;455/12.1,13.1,31.1,54.1,54.2,56.1,422,427,428,429,430,450,452,453,455
;379/58,59 ;370/316 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Le; Thanh
Attorney, Agent or Firm: McGurk; Harold C.
Claims
What is claimed is:
1. A method for assigning a subscriber unit to a visited gateway,
the method comprising the steps of:
a) receiving a connection request;
b) forwarding the connection request to a home gateway and
selecting an alternate home gateway if the home gateway is
incapable of servicing the connection request;
c) selecting the visited gateway from a list of gateways to service
the connection request;
d) forwarding the connection request to the visited gateway;
and
e) setting-up a call.
2. A method as recited in claim 1, wherein step (a) comprises the
steps of:
a1) a subscriber unit transmitting the connection request to a
currently serving satellite; and
a2) the currently serving satellite receiving the connection
request.
3. A method as recited in claim 1, wherein step (b) comprises the
steps of:
b1) the currently serving satellite determining whether the home
gateway is capable of servicing the connection request;
b2) the currently serving satellite selecting an alternate home
gateway if the home gateway is incapable of servicing the
connection request; and
b3) the currently serving satellite routing the connection request
to the home gateway.
4. A method as recited in claim 1, wherein the subscriber unit sent
the connection request for the call, and wherein step (c) comprises
the step of selecting the visited gateway from a list of gateways
based on at least one of the following: where the subscriber unit
is located, whether the visited gateway is capable of servicing the
connection request, and whether the call is to be intercepted.
5. A method as recited in claim 1, wherein the subscriber unit sent
the connection request for the call, and wherein step (c) comprises
the step of selecting the visited gateway from a list of gateways
based on if the call is to be intercepted.
6. A method as recited in claim 1, wherein the subscriber unit sent
the connection request for the call, and wherein step (c) comprises
the step of selecting the visited gateway from a list of gateways
based on if the visited gateway is capable of servicing the
connection request.
7. A method as recited in claim 1, wherein the subscriber unit sent
the connection request for the call, and wherein step (c) comprises
the step of selecting the visited gateway from a list of gateways
based on if the visited gateway is not overloaded, not down and not
reaching maximum capacity.
8. A method as recited in claim 1, wherein step (c) comprises the
step of the home gateway selecting the visited gateway to service
the connection request.
9. A method as recited in claim 1, wherein the visited and home
gateways are part of a network of nodes, step (d) comprises the
step of forwarding the connection request through some of the
network of nodes.
10. A method as recited in claim 1, wherein step (c) comprises the
steps of:
c1) the home gateway selecting the visited gateway; and
c2) the home gateway setting-up the call according to the
connection request if the home gateway selected itself to be the
visited gateway.
11. A method for assigning a subscriber unit to a visited gateway,
the method comprising the steps of:
a) receiving a connection request;
b) forwarding the connection request to a home gateway;
c) selecting the visited gateway from a list of gateways to service
the connection request;
d) forwarding the connection request to the visited gateway;
e) setting-up a call;
f) determining whether the visited gateway is capable of servicing
the connection request;
g) selecting an alternate visited gateway from a list of alternate
visited gateways; and
h) forwarding the connection request to the alternate visited
gateway.
12. A method as recited in claim 11, further comprising the steps
of:
i) determining whether the alternate visited gateway is capable of
servicing the connection request;
j) rejecting the connection request if the alternate visited
gateway is incapable of servicing the connection request; and
k) the alternate visited gateway setting up the call.
13. A method as recited in claim 11, further comprising the steps
of:
i) determining whether the alternate visited gateway is capable of
servicing the connection request;
j) selecting another alternate visited gateway from a list of
alternate visited gateways if the alternate visited gateway is
incapable of servicing the connection request;
k) forwarding the connection request to the another alternate
visited gateway if the alternate visited gateway is incapable of
servicing the connection request;
l) repeating steps (j) and (k) until an alternate visited gateway
is found that can service the connection request or until steps (j)
and (k) are repeated a predetermined number of times;
m) rejecting the connection request if the alternate visited
gateway is incapable of servicing the connection request or steps
(j) and (k) are repeated the predetermined number of times; and
n) the alternate visited gateway selected in step (j) setting up
the call.
14. A method as recited in claim 11, further comprising the steps
of:
i) determining whether the alternate visited gateway is capable of
servicing the connection request;
j) selecting another alternate visited gateway from a list of
alternate visited gateways if the alternate visited gateway is
incapable of servicing the connection request;
k) forwarding the connection request to the another alternate
visited gateway if the alternate visited gateway is incapable of
servicing the connection request;
l) rejecting the connection request if the alternate visited
gateway is incapable of servicing the connection request; and
m) the another alternate visited gateway setting up the call.
15. A method for assigning a subscriber unit to a visited gateway,
the method comprising the steps of:
a) receiving a connection request;
b) forwarding the connection request to a home gateway;
c) determining whether the home gateway is capable of servicing the
connection request;
d) selecting an alternate home gateway if the home gateway is
incapable of servicing the connection request;
e) forwarding the connection request to the home gateway or the
alternate home gateway selected in step (d);
f) selecting the visited gateway from a list of gateways to service
the connection request;
g) forwarding the connection request to the visited gateway;
h) determining whether the visited gateway is capable of servicing
the connection request;
i) selecting an alternate visited gateway from a list of alternate
visited gateways if the visited gateway is incapable of servicing
the connection request;
j) forwarding the connection request to the alternate visited
gateway if the visited gateway is incapable of servicing the
connection request; and
k) setting-up a call.
16. A method as recited in claim 15, wherein the subscriber unit
sent the connection request for the call, and wherein step (f)
comprises the step of selecting the visited gateway from a list of
gateways based on at least one of the following: where the
subscriber unit is located, whether the visited gateway is capable
of servicing the connection request, and whether the call is to be
intercepted.
17. A method as recited in claim 15, wherein the subscriber unit
sent the connection request for the call, and wherein step (f)
comprises the step of selecting the visited gateway from a list of
gateways based on if the call is to be intercepted.
18. A method as recited in claim 15, wherein the subscriber unit
sent the connection request for the call, and wherein step (f)
comprises the step of selecting the visited gateway from a list of
gateways based on if the visited gateway is capable of servicing
the connection request.
19. A method as recited in claim 15, wherein the subscriber unit
sent the connection request for the call, and wherein step (f)
comprises the step of selecting the visited gateway from a list of
gateways based on if the visited gateway is not overloaded, not
down and not reaching maximum capacity.
20. A method as recited in claim 15, further comprising the steps
of:
l) determining whether the visited gateway is capable of servicing
the connection request;
m) selecting an alternate visited gateway from a list of alternate
visited gateways; and
n) forwarding the connection request to the alternate visited
gateway.
21. A method as recited in claim 20, further comprising the steps
of:
o) determining whether the alternate visited gateway is capable of
servicing the connection request;
p) rejecting the connection request if the alternate visited
gateway is incapable of servicing the connection request; and
q) the alternate visited gateway setting up the call if the
connection request is not rejected in step (p).
22. A method as recited in claim 20, further comprising the steps
of:
o) determining whether the alternate visited gateway is capable of
servicing the connection request;
p) selecting another alternate visited gateway from a list of
alternate visited gateways if the alternate visited gateway is
incapable of servicing the connection request;
q) forwarding the connection request to the another alternate
visited gateway if the alternate visited gateway is incapable of
servicing the connection request;
r) repeating steps (p) and (q) until an alternate visited gateway
is found that can service the connection request or until steps (p)
and (q) are repeated a predetermined number of times;
s) rejecting the connection request if the alternate visited
gateway is incapable of servicing the connection request or steps
(p) and (q) are repeated the predetermined number of times; and
t) the another alternate visited gateway selected in step (p)
setting up the call.
23. A method as recited in claim 20, further comprising the steps
of:
o) determining whether the alternate visited gateway is capable of
servicing the connection request;
p) selecting another alternate visited gateway from a list of
alternate visited gateways if the alternate visited gateway is
incapable of servicing the connection request;
q) forwarding the connection request to the another alternate
visited gateway if the alternate visited gateway is incapable of
servicing the connection request;
r) rejecting the connection request if the alternate visited
gateway is incapable of servicing the connection request; and
s) the another alternate visited gateway setting up the call.
24. A method for assigning a subscriber unit to a visited gateway,
the method comprising the steps of:
a) a currently serving satellite receiving a connection
request;
b) the currently serving satellite forwarding the connection
request to a home gateway;
c) the currently serving satellite determining whether the home
gateway is capable of servicing the connection request;
d) the currently serving satellite selecting an alternate home
gateway if the home gateway is incapable of servicing the
connection request;
e) the currently serving satellite forwarding the connection
request to the home gateway or to the alternate home gateway
selected in step (d);
f) the home gateway selecting the visited gateway from a list of
gateways to service the connection request;
g) the home gateway forwarding the connection request to the
visited gateway;
h) the visited gateway determining whether the visited gateway is
capable of servicing the connection request;
i) the visited gateway selecting an alternate visited gateway from
a list of alternate visited gateways if the visited gateway is
incapable of servicing the connection request;
j) the visited gateway forwarding the connection request to the
alternate visited gateway if the visited gateway is incapable of
servicing the connection request;
k) the visited gateway setting-up a call if the visited gateway is
capable of servicing the connection request; and
l) the alternate visited gateway setting-up the call if the visited
gateway is incapable of servicing the connection request.
Description
TECHNICAL FIELD
This invention relates generally to mobile telecommunication
systems and, in particular, to methods for assigning subscriber
units to visited gateways.
BACKGROUND OF THE INVENTION
When a subscriber unit requests service in conventional space-based
or terrestrial telecommunication systems, the method for assigning
the subscriber unit to a gateway is typically based on which
gateway is the closest to the subscriber unit. For a subscriber
unit close to a border, the subscriber unit may be assigned to a
gateway which is on the other side of a border, rather than to a
gateway in the country in which the subscriber unit is currently
located. Moreover, the subscriber unit may be assigned to a gateway
which is down, overloaded or incapable of handling the call, and in
which case, the call may be dropped.
Another problem in conventional methods for assigning subscriber
units to gateways occurs when the subscriber unit's communication
is to be intercepted. In most systems, subscriber traffic can only
be intercepted at the gateway which is providing service to the
subscriber unit. However, the information about which calls are to
be intercepted usually reside in a gateway which is expected to
provide service to the subscriber. Thus, if the subscriber unit is
located in another country which contains another gateway, and the
other gateway is not capable of intercepting the subscriber unit's
call, the call would not be intercepted if the subscriber unit was
assigned to this other gateway. In addition, the system would not
know that the call was to be intercepted because it did not consult
the subscriber unit's home gateway for the intercept status of the
call.
Thus, there is a significant need for methods that assign a
subscriber unit to a gateway that can best service it. There is
also a significant need for a method that assigns a specific
subscriber unit to a serving gateway based on whether the call is
to be intercepted or whether the call is to be routed around
disabled or congested gateways.
In addition, there is significant need for a method that assigns
subscriber units that would have been dropped due to gateway
congestion or failure to an alternate home or visited gateway.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a general view of a space-based mobile
telecommunication system according to a preferred embodiment of the
present invention;
FIG. 2 shows a general view of the components of a satellite, home
and visited gateways according to preferred embodiment of the
present invention; and
FIG. 3 shows a flowchart of a method for assigning a subscriber
unit to a visited gateway according to a preferred embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention has utility in that a home gateway assigns a
subscriber unit to a visited (i.e., serving) gateway to service the
subscriber unit's connection request and call. Moreover, the
present invention allows a subscriber unit to be served by a
gateway other than the gateway which is geographically closest
based on factors such as whether the call is to be intercepted, for
example.
A "satellite" as used throughout this description means a manmade
object or vehicle intended to orbit the earth. A "satellite"
comprises geostationary, low-earth and medium-earth orbiting
satellites and/or combinations thereof. A "constellation" means a
number of satellites arranged in orbits for providing specified
coverage (e.g., radio communication, remote sensing, etc.) of a
portion, portions or all of the earth. A constellation typically
includes multiple rings (or planes) of satellites and may have an
equal number of satellites in each plane, although this is not
essential. The terms "cell", "beam" and "antenna pattern" are not
intended to be limited to any particular mode of generation and
include those created by either terrestrial or space-based
telecommunication systems and/or combinations thereof.
FIG. 1 shows a general view of space-based telecommunication system
10 according to a preferred embodiment of the present invention.
Although FIG. 1 illustrates a highly simplified diagram of mobile
telecommunication system 10, system 10 comprises at least one
satellite 20, any number of subscriber units 30 and at least two
gateways 40. Generally, telecommunication system 10 may be viewed
as a network of nodes. All nodes of communication system 10 are or
may be in data communication with other nodes of communication
system 10 through communication links. In addition, all nodes of
telecommunication system 10 are or may be in data communication
with other telephonic devices dispersed throughout the world
through public service telephone networks (PSTNs) and/or
conventional terrestrial communication devices coupled to a PSTN
through conventional terrestrial base stations.
The present invention is applicable to space-based
telecommunication systems that assign particular regions on the
earth to specific cells on the earth, and preferably to systems
that move cells across the surface of the earth. Although the
present invention is applicable to space-based telecommunication
systems 10 having at least one satellite 20 in low-earth,
medium-earth or geosynchronous orbit, satellite 20, is preferably
in low-earth orbit around earth. Satellite 20 may be a single
satellite or one of many satellites in a constellation of
satellites orbiting earth. The present invention is also applicable
to space-based telecommunication systems 10 having satellites 20
which orbit earth at any angle of inclination including polar,
equatorial, inclined or other orbital patterns. The present
invention is applicable to systems 10 where full coverage of the
earth is not achieved (i.e., where there are "holes" in the
telecommunication coverage provided by the constellation) and to
systems 10 where plural coverage of portions of the earth occur
(i.e., more than one satellite is in view of a particular point on
the earth's surface).
Each satellite 20 communicates with other nearby satellites 20
through cross-links. These cross-links form a backbone of
space-based mobile telecommunication system 10. Thus, a call or
communication from one subscriber unit located at any point on or
near the surface of the earth may be routed through a satellite or
a constellation of satellites to within range of substantially any
other point on the surface of the earth. A communication may be
routed down to a subscriber unit (which is receiving the call) on
or near the surface of the earth from another satellite 20. How
satellite 20 physically communicates (e.g., spread spectrum
technology) with subscriber units 30 and gateway 40 is well known
to those of ordinary skill in the art.
Subscriber units 30 may be located anywhere on the surface of earth
or in the atmosphere above earth. Mobile telecommunication system
10 may accommodate any number of subscriber units 30. Subscriber
units 30 are preferably communication devices capable of receiving
voice and/or data from satellites 20 and/or gateway 40. By way of
example, subscriber units 30 may be hand-held, mobile satellite
cellular telephones adapted to transmit to and receive
transmissions from satellites 20 and/or gateway 40. Moreover,
subscriber units 30 may be computers capable of sending email
messages, video transmitters or facsimile machines just to name a
few.
How subscriber units 30 physically transmit voice and/or data to
and receive voice and/or data from satellites 20 is well known to
those of ordinary skill in the art. In the preferred embodiment of
the present invention, subscriber units 30 communicate with
satellite 20 using a limited portion of the electromagnetic
spectrum that is divided into numerous channels. The channels are
preferably combinations of L-Band, K-Band and/or S-band frequency
channels but may encompass Frequency Division Multiple Access
(FDMA) and/or Time Division Multiple Access (TDMA) and/or Code
Division Multiple Access (CDMA) communication or any combination
thereof. Other methods may be used as known to those of ordinary
skill in the art.
Gateway 40 communicates with and controls satellite 20. There may
be multiple gateways 40 located at different regions on the earth.
For example, there may be one gateway 40 located in Honolulu,
another located in Los Angeles and another in Washington, D.C.
Another example is to have separate gateways 40 located in each
country on the earth. Gateways 40 may provide satellite control
commands to satellite 20 so that satellite 20 maintains its proper
position in its orbit and performs other essential house-keeping
tasks. Gateways 40 may be additionally responsible for receiving
voice and/or data from satellite 20. How gateway 40 physically
communicates (e.g., spread spectrum) with satellites 20 and/or
subscriber units 30 is well known to those of ordinary skill in the
art.
A "gateway" 40 as referred to throughout this description includes
home gateways, visited gateways, alternate home gateways, alternate
visited gateway, ground stations, ground control stations, base
stations, earth terminals or any other term representing a facility
that determines which satellite or base station should service a
particular subscriber unit.
FIG. 2 shows a general view of the components of satellite 20
and/or gateway 40 according to a preferred embodiment of the
present invention. For purposes of this description, reference will
be made to satellite 20, although most of the components are
similar to those in gateway 40. Satellite 20 comprises at least the
following components: antenna 21, transceiver 22, processor 23 and
memory 24. There may be other components of satellite 20 that are
not shown which are necessary for operating a satellite but are not
important to the present invention. These other components are well
known to those of ordinary skill in the art, including for example,
solar arrays and fuel propulsion system in satellites 20, or
switches and network routers in gateways 40. Moreover, there may be
more than one of the components in satellite 20, such as multiple
processors 23, for example.
Antenna 21 of satellite 20 is coupled to transceiver 22, while
transceiver 22, processor 23 and memory 24 are inter-coupled to
each other. Transceiver 22 is able to transmit or receive data or
voice, and may be for example, a modem. Transceiver 22 is also
capable of receiving data from subscriber units 30 and/or gateway
40. Processor 23, via a software program controls the operation of
satellite 20 and the other components of satellite 20. Memory 24
stores part of the software executable version of method 100
(described below) and other software programs. Antenna 21,
transceiver 22, processor 23 and memory 24 are all well known to
those of ordinary skill in the art.
FIG. 3 shows a flowchart of method 100 for assigning subscriber
units to visited gateways according to a preferred embodiment of
the present invention. Method 100 is a software program that is
executed by a number of network components (e.g., currently serving
satellite, home gateway, alternate home gateway (if needed),
visited gateway and alternate visited gateway (if needed)) in the
preferred embodiment. The network components may execute other
software programs as well.
Method 100 begins in step 102 when a subscriber unit accesses the
network 10 and sends a connection request to a satellite currently
serving it. The connection request includes information about the
subscriber unit, including for example, a location of the
subscriber unit on earth, a home gateway identification (ID) and a
priority of the call, such as whether the call is an emergency
call.
The currently serving satellite determines in step 104 whether the
home gateway is capable of handling the connection request. The
determination is based on whether the home gateway is down,
overloaded or some other factor that makes it incapable of handling
the connection request. The status of each gateway, including the
home gateway, is stored in each satellite and is periodically
updated in one or more satellites whenever the status of a gateway
changes.
If the home gateway is incapable of servicing the connection
request, the currently serving satellite determines in step 106
which alternate home gateway will service the connection request.
The currently serving satellite chooses an alternate home gateway
from an alternate list of home gateways. It is preferred that there
be at least one alternate home gateway for each home gateway.
However, in alternative embodiments, there may be no alternate home
gateways due to political considerations or nationalist concerns,
for example; however, the number of home gateways may be equal to
the total number of gateways in the system. In the preferred
embodiment, the currently serving satellite selects an alternate
home gateway based on which alternate home gateway is the next best
choice in the list of alternate home gateways. The next best choice
is based on whether the alternate home gateway has the capability
to handle the call. If the currently serving satellite knows that
the alternate home gateway is also incapable of servicing the
connection request for any reason, the currently serving satellite
may choose another alternate home gateway from the list of
alternate home gateways.
In the preferred embodiment, an alternate home gateway will be
chosen in step 106. However, in an alternative embodiment, if an
alternate home gateway is not chosen (because no other gateway can
handle the request), method 100 skips to step 124 and rejects the
connection request. This step may involve sending a message to the
subscriber unit that indicates to the subscriber unit that the
connection request is rejected.
If an alternate home gateway is chosen by the currently serving
satellite, the alternate home gateway ID is substituted for the
original home gateway ID in the connection request. The currently
serving satellite and the other satellites in the network use the
home gateway ID contained in the connection request to route the
connection request to the subscriber unit's home gateway.
If the home gateway is capable of handling the connection request
as determined in step 104 or an alternative home gateway is
selected in step 106, the currently serving satellite adds its own
ID to the connection request and forwards or routes in step 108 the
revised connection request to the home gateway. If the currently
serving satellite is directly coupled to the home gateway, the
satellite routes the information down to the home gateway.
Otherwise, the connection request has to be routed through the
network of satellites. As described above, the satellites are
interconnected to each other by cross-links. A table or other data
structure resides in each satellite so that the connection request
can be routed from the currently serving satellite through other
intermediary satellites if needed, and finally to the satellite
that is directly servicing the home gateway.
According to FIG. 3, after the home gateway receives the connection
request in step 108, the home gateway selects in step 110 a serving
gateway from a list of gateways that are capable of servicing the
connection request. The gateway selected to be the serving gateway
may be the home gateway or may be another gateway. If the gateway
selected to be the serving gateway is not the home gateway, it is
referred to as a visited gateway. In the preferred embodiment, the
selection made by the home gateway is based on a few factors: where
the subscriber unit is located (as contained in the connection
request), whether the serving gateway is capable of handling the
connection request, and whether the call is to be intercepted.
There may be other factors known to those of ordinary skill in the
art that may be incorporated into selecting the serving
gateway.
Each gateway monitors its congestion level to determine whether it
is capable of handling the connection request. The gateway status
information, which includes the congestion level, is transmitted
periodically or upon transitions to the satellites and other
gateways in the system. Some gateways may be down or overloaded.
Each gateway monitors its congestion level by determining if it
wants more or less connection requests. If a gateway exceeds its
maximum congestion level, it signals to the satellites and the
other gateways that it will be unable to service any more
connection requests. Each satellite and gateway receiving this
message updates its gateway status information to indicate that the
gateway is a poor choice. Conversely, when gateway determines that
it can handle more calls, the gateway signals to the satellites and
other gateways that it can handle more connection requests. Upon
receipt of this message, each satellite and gateway updates its
gateway status information to make the gateway more of a preferred
choice.
Each home gateway also stores information about whether a
particular subscriber unit's call is to be intercepted, and which
gateway is to perform the intercept function. If the subscriber
unit is to be intercepted, the home gateway assigns a serving
gateway that is capable of intercepting the call. In some systems,
a subscriber unit may only be intercepted at the home gateway. In
such a case, it is important that the home gateway selects itself
to service the call. In other systems, a subscriber unit's call may
be intercepted at any gateway. In such a situation, any of the
visited gateways can be selected to intercept the call.
Once the home gateway selects a visited gateway in step 110 in FIG.
3, the home gateway forwards or routes in step 112 the gateway
assignment to the visited gateway. In an alternative embodiment,
the home gateway before step 112 may first determine if it selected
itself to be the serving gateway. If the home gateway selected
itself, method 100 skips steps 112 and 114 and sets up the call
between the subscriber unit and satellite (as performed in step 116
and further discussed below). Once the visited gateway receives the
gateway assignment in step 112, the visited gateway decides in step
114 whether to accept or reject the connection request. If the
visited gateway decides not to accept the call for a reason
associated with this gateway (i.e., a reason that would not
preclude another gateway from servicing the call), the visited
gateway selects in step 118 an alternate visited gateway from an
ordered list of preferred alternate visited gateways. This list
includes all other possible gateways that can service the call.
Once the alternate visited gateway is selected in step 118, the
connection request is forwarded to the alternate visited gateway in
step 120.
The alternate visited gateway decides in step 122 if it wants to
accept or reject the connection request. If the alternate visited
gateway accepts the connection request, the alternate visited
gateway sets up the call in step 116. Otherwise, the alternative
request is rejected and the call is dropped in step 124. Step 124
may include the step of sending a reject message to the subscriber
unit that indicates that the connection request is being rejected.
In an alternative embodiment, method 100 determines whether the
connection request has been forwarded a predetermined number of
times. If the connection request was forwarded less than the
predetermined number of times, method 100 repeats steps 118, 120
and 122 until it either sets up the call in step 116 or exceeds the
predetermined number of times of forwarding the call and eventually
rejects the call in step 124.
Call setup as performed in step 116 requires that the visited
gateway signal the currently serving satellite with synchronization
information so that the subscriber unit and the currently serving
satellite can communicate with each other. Call setup procedures
are well known to those of ordinary skill in the art. Once the call
is setup in step 116 or rejected in step 124, method 100 ends.
It will be appreciated by those skilled in the art that the present
invention includes a method where a home gateway selects a serving
gateway based on the location of the subscriber unit, whether the
call is to be intercepted and whether the serving gateway is
capable of servicing the connection request. Thus, it is an
advantage of the present invention to assign a specific subscriber
unit to a serving gateway for the purpose of intercepting the
subscriber traffic. Another advantage of the present invention is
that a call is not dropped because the visited gateway initially
assigned by the home gateway is unable to service the connection
request. Yet another advantage of the present invention is that
connection requests are routed around disabled or congested
gateways. An additional advantage of the present invention is that
connection requests that would have been dropped due to gateway
congestion or failure are now served by an alternate gateway.
Another advantage is that a subscriber unit can be served by any
one of a number of alternate gateways.
Accordingly, it is intended by the appended claims to cover all
modifications of the invention which fall within the true spirit
and scope of the invention.
* * * * *